inclined metal formwork(3).
The final pour, for the face wall, is carried out in a single full height operation along lengths of 28ft. 6in. This difficult pour was initially accom- plished by erecting the front face of the shutter in 2ft. 6in. high sections as the pour progressed. While this system worked satisfactorily, savings were made later by increasing the size of the sections from 2ft. 6in. to 5ft. in height and then to 10ft. This was made prac- ticable because of the skills developed through the repetitive use of the shut- ter and also because of special aids, such as workability additives in the concrete and perspex observation win- dows fixed in the shutter face.
The large number of identical units in the reservoir made it feasible to have complete cages of reinforcement assembled at a factory off site. The cages are fabricated quickly, using
electrical welding techniques to posi- tion bars, and then transported to the site where they are placed directly in the formwork.
Although most of the perimeter wall is formed by the 57ft. long modular units, a draw-off chamber, access ramps and other ancillary struc- tures are also incorporated within the wall structure. In order to preserve the amenity value of the site, which is on the banks of the River Thames, an earth embankment is being construct- ed against the outside of the wall units; this will be grassed over and planted with shrubs.
Waterproofing
The most novel part of the project is the floor waterproofing layer which is formed by a lining of butyl rubber sheeting, 60 thou. of an inch (1.52 mm) thick. Sheets of the material
chosen because it is tough and does not degrade will be delivered to the site in rolled sections each weighing 11⁄2 tons; these will be laid across the floor on a bed of sand. Adjacent sheets will then be vulcanised together and the whole connected to the base of the perimeter wall.
Butyl rubber, as a waterproofing membrane, has not before been used on such a scale in Europe.
The reservoir was designed by John Taylor and Sons, London, consulting engineers, in collaboration with the chief engineer of the Working and Dis- trict Water Company, Mr. F.E.W. Barnes.
Below-top: Preparation for fixing the top of the inclined shuttering for a modular wall unit. Bottom: Access ramp. At the bottom of the wall section is the main water bar. When the butyl sheeting is in position over the floor, it will be fixed to the water bar to seal the reservoir completely.
Far East BUILDER, May 1970
KINZANI
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